Harmonic analyzer and switching mechanism therefor



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THERBFQR 2 Sheets-Sheet l R. l.. wEGEL ET AL iled Jan. 25, l1923 HARMONIC ANALYZER AND SWITCHING MECHANISM Patented Apr. 7, 1931 UNITED STATES PATENT OFFICE RAYMOND L. WEGEL, OF NEW YORK, N. Y., AND CHARLES R. MOORE, OF MAPLEWOOID, NEW JERSEY, ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION OF NEW YORK HARMONIC ANALYZER AND SWITCHING MECHANISM THEREFOR Application filed January 23, 1923. Serial No. 614,503.

This invention relates to harmonic analyzers and more particularly to switching mechanism for controlling the operation of a harmonic analyzer or the like.

An object of the invention is to provide means for rapidly performing a plurality of switching operations on an electric circuit without introducing errors in the electric characteristics of the circuit.y

In a harmonic analyzer Ysuch as that described by Pupin, Resonance analysis of alternating and polyphase currents, Trans. A. I. E. E., May 1894, Vol. XI, page 523, a tuned circuit is provided for selecting a ysingle frequency component of a complex wave to be analyzed, and the circuit is sucsively tuned to different frequencies throughout a desired range for determining the relative amplitudes of the frequencies comprised in the wave. Where it is desired to make a large number of frequency readings it is of advantage to be able to change rapidly from one setting to another, partly to save time and partly to avoid errors due to the difficulty of maintaining constant for a long period the source of the wave being analyzed. Furthermore, the switching leads extending to the reactances to be connected into the tuned circuit must be short to avoid introducing capacity. It has been found impracticable to employ electric relays adjacent the elements of the tuned circuit on account of currents induced in the circuit by the relays.

' 1n accordance with this invention a number of pneumatic or air relays are employed which have electrical contacts connected by short leads to a set of condensers. The operation of the air relays is controlled from a distant point by a perforated sheet of paper similar to those used in automatic pianos. Air relays are also employed for controlling the rewinding and stopping of the perforated sheet and also for controlling other operations such as recording the analysis of the wave.

It is sometimes desirable to compare a complex wave in one piece of apparatus with a wave in some other piece of apparatus. The inventionprovides means for alternately connecting two electric sources to the analyzer,

with sufficient rapidity to obtain simultaneous records of the frequency content of both.

Further objects of the invention will be apparent from the following detailed description and claims taken in connection with the accompanying drawings of which Fig. 1 is a schematic view of an apparatus embodying the invention; Fig. 2 is a detail view showing one air relay in elevation and a second air relay in section; Fig. 3 is a sectional view taken on the line 3-3 of Fig. 2; Fig. 4 is a schematic view of a modified form of tuned circuit; and Fig. 5 shows a portion of a photographic record produced bv the apparatus.

Referring to the drawing by reference numerals, input terminals 10 and 11 are adapted to be connected to an electric source to be analyzed. Leads extend from terminals 10 and 11 to a tuned or, more properly, a filter circuit comprising a shunt resistance 12 of a low value, a series inductance 13 and a shunt variable condenser 14 in the order named. The variable condenser 14 comprises a plurality of condenser elements 15. In one embodiment of the invention, twenty-live condenser elements were employed capable of Y being connected into the circuit, in such combinations as to give the variable condenser 14 over one million different values and thereby to tune the circuit to a corresponding number of frequency settings. Connected across the condenser 14 is an amplifier rectiiier 17 and the rectified current is applied to a galvanometer 19, comprised in a recording camera 20.

This camera is similar to the camera described in the patent issued to J. T. L. Brown, Patent No. 1,536,768 issued May 5, 1925 for testing systems, and will be only briefly described here. Light from a lamp 21 is reflected from a mirror 22 mounted on the moving coil of galvanometer 19, through a cylindrical lens 23 and on to a sensitive strip 24. The galvanometer 19 has a natural frequency higher than the rate of change from one frequency to another but lower than the lowest frequency to be examined. It is Aalso critically damped. The distance of the beam of light from the edge of the paper will be proportionate to the amplitude of the particular frequency bel-N v los ing selected, amplified and rectified. A series of lamps 26 only one of which is shown in the drawing is employed for producing longitudinal lines upon the sensitive strip 24. For producing transverse lines, lamp 28 is provided which is periodically energized at certain successive frequency settings of the analyzer.

For putting switching condenser elements 15 into and out of circuit, air relays 30 are provided. Each relay comprises vacuum chambers 32 and 33, one side of each being formed of a flexible diaphragm 34. A contact controlling member 35 is operated by movements of the 'diaphragm 34 for opening and closing a contact 36 in series with a respective condenser element 15. The vacuum chambers 32 and 33 are connected by tubes 37 to avacuum header 39 and also to a tracker .bar 41 having openings normally closed to the atmosphere by a paper roll 43, which has perforations adapted at times to admit atmospheric pressure to the tubes 37. In the particular apparatus referred to above, the roll 43 was provided with perforations giving combinations of capacity corresponding to about 1500 frequency settings between 80 cycles and 5000 cycles. The perforated roll 43 is Wound and rewound by a suitable air motor 45. A vacuum pump 47 is connected to the header 39 through a valve 49 and is also connected to an auxiliary vacuum header 5l. When the pump is in operation vacuum is maintained at all times in header 51. At cer- 35 tain times, however, valve 49 is operated to admit atmospheric pressure to header 39 and for this reason air motor 45 is connected to the auxiliary header 51.

The electric control apparatus will be best understood from a description of its operation. Assuming that a source of current to be analyzed, such as indicated at 53 or 55, has been connected to the input terminals, 10 and 11, or is in position to be connected automatically. The operator momentarily closes a key 57 thus completing a circuit through relays 59 and 60. Contact 61 of relay 59 closes a circuit for a motor 62 which drives the sensitive strip 24 and for motor 64 which drives the pump 47. It also closes the circuit for lamps 21 and 26. While separate grounded batteries are shown for convenience in reading the drawing, it is to be understood that a single source of current is preferably used.

As soon as motor 64 starts a substantial vacuum is produced in headers 39 and 5l, and air motor 45 then starts the perforated roll 43 in operation. In parallel with key 57 is a contact 66, which is now closed by the operation of an air relay 68. This relay is similar to relay 30 but has only one operating chamber and its controlling member 35 is connected to the diaphragm 34 for positive operation in both directions. When the paper is at rest and before the machine starts, a hole in the paper is so situated as to let air into the relay 68. This maintains contact 66 open. As soon as the paper starts to move over the tracker bar 41 the hole passes ofi'l and relay 68 is exhausted closing contact 66. Key 57 may then be released and power will continue to be supplied until the paper is completely unwound and reWound and the hole, which was orig-inally in communication with air relay 68 again reaches the tracker bar. Air is then let into relay 68 and contact 66 opened and all of the apparatus will come to rest.

When relay 59 opera-tes to put the apparatus in motion, relay 60 also closes its contact and connects battery to one side of lamp 28. An air relay 70 having one vacuum chamber is in communcation at times with holes in the perfo-rated sheet 43 corresponding to certain frequency settings of the condenser 14. I/Vhen one of these openings is opposite the passage leading to air relay 70, a contact 72 is closed, momentarily lighting lamp 28. This sends a beam of light extending the full length of lens 23 and produces a transverse line on sensitive strip 24. In order that the flash may be brief and of constant duration, electrical relay 74 opens the circuit for the lamp as soon as current begins to flow. In the embodiment of the invention above referred to, transverse lines were drawn every 20 cycles from 80 to 400 cycles, every 50 cycles from 400 to 1000 cycles and every 100 cycles from 1000 to 5000 cycles.

The frequency settings of the tuned circuit are also spaced farther apart as the frequency increases, for the reason that the circuit is not so sharply tun-ed at the higher frequencies. In general the higher components of frequency -sources to be analyzed are more widely spaced than the lower components, and the arrangement just described permits a complete analysis to be made with a much shorter perforated roll than would be required if the frequency settings were equally spaced.

While the tracker bar terminals of tubes 37 are closed by the paper 43, both diaphragms of a given relay 30 are retracted and controlling member 35 is held by friction in any given position. Assuming that controlling member 35 is in position to hold contact 36 open and that for a given frequency it is desired to close the contact, a hole in paper 43 admits atmospheric pressure to chamber 32 and a spring (described later in connection with Figs. 2 and 3) causes a movement of diaphragm 34 and controlling member 35 to close the contact 36. As soon as the hole passes the tracker bar, chamber 32 i-s again evacuated, but contact 36 remains closed as long as the associated condenser 15 is needed in successive frequency settings. When the condenser is no longer needed, air is momentarily admitted to chamber 33 and contact 36 is opened.

When the roll of paper 43 has been completely unwound, an opening in the roll permits air to enter the chamber 32 of an air relay 76. This closes contact 78, connecting ground to relay which is energized and closes contact 81. This energizes a solenoid 82 for reversing the gear connection between the motor 45 and the paper roll 43. Relay 80 also closes a contact 84, energizing a solenoid 85, which operates valve 49 to cut off the connection from the pump to the vacuum header` 39 and at the same time opening the header to the atmosphere. This is done for the reason that the paper rewinds much faster than it unwinds and if vacuum were applied to all the openings in tracker bar 41 there would be too great a drag on the paper. Relay 80 also opens contact 87 thus cutting off lamps 21 and 26.

When the paper has been completely rewound air is admitted to the other chamber 33 of air relay 76 and Contact 78 is again opened. This occurs simultaneously with the opening of contact 66 by the operation of relay 68. It Will be noted that air relay 68 and the chamber 33 of relay 76 are connected to the header 51 since they are required to operate at a time when header 39 is not evacuated. Contacts 78 are so arranged as to be open when the contact controlling member of relay 76 is in its left hand position and also in its midposition.

If at any time it is desired to reverse the operation of the apparatus before the roll 43 is completely unwound, a valve 89 may be opened admitting air to chamber 32 of relay 76. The remainder of the operation is then the same as just described for the full automatic action.

The complete apparatus with the exception of the pump may be stopped at any point by closing key 91. This key closes a circuit through relay 93 which opens contact 94 and stops motor 62. This also energizes relay 80, breaking the circuit of lamps 21 and 26. This, however, does not operate solenoids 82 and since their circuits are already broken at contact 94. At the same time, air motor 45 is stopped by a clamp 95, connected to key 91, which closes the passage leading from the motor to the auxiliary header 51.

When it is desired to compare the wave produced by two pieces of apparatus, such as those indicated at 53 and 55, terminals 10 and 11 may form a part of a reversing switch for alternately connecting the sources to the analyzer. As shown, two air relays 96 and 97 are provided, having their opposite chambers connected together so that when one relay opens its contact the other relay closes its contact. Openings in paper 43 admit air i to these pairs of chambers alternatingly with source may be obtained, and since the curves are obtained simultaneously it can easily be assured that the two pieces of apparatus are working under similar conditions. Fig. 5

represents a curve obtained by connecting the tuned circuit alternately to two portions of the same circuit and shows clearly the relative amplitudes of the various frequencies in each portion of the circuit.

Referring to Fig. 2, the elements comprised in the tuned circuit are mounted in a moisture proof boX 99. Air relays 30 are mounted on the side of the boX with contacts 36 inside. @ne spring of each pair of contacts 36 is connected through a contact 100 to one side of the tuned circuit, while the other spring is connected through a contact 101 to the corresponding condenser l5.

An elliptical spring 103 is connected to both diaphragms 34 of each air relay in such a way as to draw them toward each other. A plunger 104 is carried by each diaphragm for operating the contact controlling member 35. The outside wall of each vacuum chamber is in the form of a recessed disc 105 having an annular groove 106 which insures the retraction of the plungers to their rearward limit of motion. Disc 105 and diaphragm 34 are clamped in position by a screw threaded ring 107. The operation of each relay may be observed by means of a window 108.

`With the apparatus above described, in which about 1500 frequency settings were made in a. range of from 60 cycles to 5000 cycles, the full range can be covered in a period of five minutes, whereas if the switching operations had to be done by hand the task would require several hours with the attendant danger that the conditions being tested would not remain uniform.

In Fig. 4 is shown a tuned circuit which may be substituted for the one shown in Fig. 1. In this arrangement, a corrective network comprising a low impedance coil 110 and a low impedance condenser 111, is placed in series with resistance 12. If the inductance 13 is given such a value that the tuned circuit is most eflicient at an intermediate portion of the frequency range to be examined, this corrective network, or an equivalent thereof, may be used to build up the transmission at the upper and lower frequencies. Inductance 110 and condenser 111 will be in resonance at the frequency at which the tuned circuit 13, 14 is most efficient, but at other frequencies their impedance is added to the shunt resistance 12.

Fig. 4 also shows one of the output conductors connected to the midpoint of resistance 12. With this arrangement a symmetrical resonance curve for a single frequency is obtained, whereas if the output voltage is taken ofi' directly across the condenser terminals or across the inductance terminals the resonance curves will be unsyinmctrical in opposite directions respectively. Where a corrective network is used with this arrangement it should be divided and placed symmetrically about resistance 12 as shown in Fig. 4.

The double acting air relay disclosed herein renders it unnecessary to use a perforated roll having long slits such as are used in` piano players. A single small perforation serves to throw a lever to one position where it remains until another perforation throws it to its original position.

While the invention has been shown in connection with a harmonic analyzer it is obvious that certain features of the invention have a wider application. For example, the quick acting pneumatic relay can be employed to an advantage wherever a rapid nonelectricV switching mechanism would be of use.

The invention claimed is:

1. A frequency selective circuit, means for changing ythe selectivity of said circuit, means for continuously operating said first means, and inea-ns vfor cyclically connecting said circuit toa plurality of sources of alternating current. v

2. A frequency selective circuit comprising an inductive reactance and a capacitive reactance, one of saidreactances being variable, pneumatic means for varying said variable rea'ctance,` means controlling said pneumatic'ineans for causing a definite sequence of frequencies to be selected, said cir.

cuit having input terminals, and means for connecting .said'terminals to a source of alternating current at alternate frequency settings and to a different source of alternating current at the remaining settings.

8. In combination, an electric circuit, a'

plurality of -reactance elements, pneumatically operated means to introduce said reactance elements into said circuit in a pre-y determined'manner, a perforated sheet for controlling said means, said means being responsive to one set of perforations in said sheet for operation'in one direction and to another set of perforations for operation in.

another direction.

4. In a s, stem for analyzing complex electric wave orms, an electric circuit comprising a plurality of impedance elements, and

pneumatic means for controlling the relation of said impedance elements to one another.

In witness'whereof, we hereunto subscribe our names this 16th day of January, A. D.

, RAYMOND L. WEGEL.

CHARLES R. MOORE. 

